/**

DatabaseUtil& db = DatabaseUtil::getInstance();
if (!db.init("config.json")) {
    std::cerr << "数据库初始化失败" << std::endl;
}

// 查询
json result = db.executeQuery("SELECT * FROM users WHERE role = 'admin'");
std::cout << result.dump(4) << std::endl;

// 插入或更新
int affected = db.executeUpdate("UPDATE users SET password = 'newpwd' WHERE username = 'admin'");
std::cout << "更新了 " << affected << " 行" << std::endl;

*/
